Yeah, this is because they havent changed their tier.
They will get the content of whatever tier they are at, not based on the amount.
This sort of thing is allowed, I would assume, because patreon started off as a tip jar platform where folks could pay the tier price or more if they wished and to this day, lots if patrons do this because they legit just want to support a creator. I have multiple patrons that send a little more than what their tier asks for, just because they want to, and I know many others who experience this as well. I can say that for most of the folks I know whom have talked about patron behaviours with me, we would not want to change/remove this ability as it is very helpful to us overall and allows patrons more control over their pledge instead of finding alternative/seperate ways to support more if patreon works for them.
This also allows folks to have multiple levels of a tier without actually having different tiers. For example, my mailed merch tier is $x amount for folks in north america but if the person is international, they need to add extra to their pledge to cover the pricier shipping. If this feature went away, no one could offer all encompassing tiers like that or other cool bonuses and I watch a lot of creators who utilize tiers like this.
Sometimes it is indeed someone not understanding they need to choose a different tier if they want a different reward so for sure, the layout and wording of the membership management could probably be better to address this.
Curious, when you say you write notes, do you re-write it every time? If you do, I would suggest writing things that you may need to send that are generally the same concept every time, into a document that you can copy/paste from. This saves a lot of time for me when I send out notes I know I’ll need to send out semi frequently that dont need to really change the wording of the initial note. (And I can always add different pleasantries or extras if it warrants it, as I send it.)
Hopefully that helps clear some things up a little. It can be frustrating because I know for me at least, many patrons dont check their notes often but it still shows them directly what rewards they are getting in the tier description on their membership page and when they try to change their amount. I will sometimes give a little bonus thing if there was a mixup because we’re all human and miss stuff, but it’s also on them to read the page explaining what they are getting for their money or asking/using the FAQ. You can provide what customer service you can to ensure that was indeed their choice but in the end, there is also only so much you can reasonably do.
If you have specifics on what part of the membership management pages you think should be changed (or ask your patrons this) that specific info would probably be super helpful to the staff here so they can really see what folks are having a hard time with.